"We assess that North Korea has followed through on its announcement by expanding its Yongbyon enrichment facility and restarting the plutonium production reactor," Clapper said.

North Korean leader Kim Jong Un signs a document regarding a long range rocket launch in this undated photo released by North Korea’s Korean Central News Agency (KCNA) in Pyongyang February 7, 2016. REUTERS/KCNA

North Korea has expanded a uranium enrichment facility and restarted a plutonium reactor that could start recovering spent fuel in weeks or months, the US intelligence chief said on Tuesday in delivering the annual assessment by intelligence agencies of the top dangers facing the country.

Director of National Intelligence James Clapper said that Pyongyang announced in 2013 its intention to refurbish and restart nuclear facilities, to include the uranium enrichment facility at Yongbyon and its graphite-moderated plutonium production reactor, which was shut down in 2007.

“We assess that North Korea has followed through on its announcement by expanding its Yongbyon enrichment facility and restarting the plutonium production reactor,” Clapper said in an opening statement to the Senate Armed Services Committee. “We further assess that North Korea has been operating the reactor long enough so that it could begin to recover plutonium from the reactor’s spent fuel within a matter of weeks to months.”

Clapper also said that Islamic militants will continue plotting against US interests overseas and homegrown attacks will pose the most significant threat from violent extremists to Americans at home. “The perceived success of attacks by homegrown violent extremists in Europe and North America, such as those in Chattanooga and San Bernardino, might motivate others to replicate opportunistic attacks with little or no warning, diminishing our ability to detect terrorist operational planning and readiness,” he said.

“ISIL involvement in homeland attack activity will probably continue to involve those who draw inspiration from the group’s highly sophisticated media without direct guidance from ISIL leadership,” he said using an acronym for the militant group. Clapper also said Iran remains the top state sponsor of terrorism, al-Qaeda-linked groups remain resilient and the US will continue to see cyber threats from China, Russia and North Korea.

Clapper said US information systems, controlled by the US government and American industry, are vulnerable to cyberattacks from Russia and China. North Korea “probably remains capable and willing to launch disruptive or destructive cyberattacks to support its political objectives,” he said.

Moscow “is assuming a more assertive cyber posture” that is based on its willingness to target critical infrastructure and carry out espionage operations even when those operations have been detected and under increased public scrutiny, Clapper said. Russia’s cyber operations are likely to target US interests in part to underpin its intelligence gathering to support Russia’s moves in the Ukraine and Syrian crises, he said.